200 THE HABITAT OF THE EURYPTERIDA 



upon crustaceous animals at all, would scarcely have used such nice 

 selection so that the eurypterids alone were consumed, while the 

 trilobites continued to nourish. 



Of a certainty, some more rational explanation must be sought. 

 This occurrence in Bohemia is one of the rare ones in the Siluric in 

 which the eurypterids are found associated with an abundant and 

 unquestionable marine fauna. Yet the facts, that no complete indi- 

 vidual has been found, that even the fragments are of so uncertain 

 a character that some which at first were supposed to belong to sepa- 

 rate species have with more study been found to belong to the same 

 species, and finally that the eurypterids, of all the myriad organisms 

 which lived in that sea, should have been broken to fragments of which 

 only a few are found — these facts will not admit of explanation on 

 the ground that the eurypterids lived in the sea. They must have 

 lived in some other aqueous realm besides the sea, and one is again 

 led to the conclusion that they must have lived in the rivers. The 

 facts of migration and the relations of the Bohemian forms to those 

 in other parts of the world strongly support this conclusion. (See 

 below chapter V). 



CHAPTER V 



The Geological and Geographical Distribution of the 

 Eurypterids and the Conditions of Migration 



summary of facts observed regarding the distribution of the 



eurypterids 



The anomalies in the geographic distribution of the eurypterids 

 constitute one of the most difficult phases of the problem of the 

 habitat. The facts which have been summarized in the tables on 

 pages 37-49, and M^hich have been discussed in various parts of the 

 paper up to this point, clearly lead to the following generalizations: 

 (1) There are many cases in which single individuals are found sepa- 

 rated geologically and geographically from other known eurypterids 

 or eurypterid-faunas. (2) The same or closely related species may 

 occur in regions widely separated, although in the same horizon, in 

 intermediate regions, either no eurypterids at all are found or else 

 those which do occur are not related to those in the other localities. 

 (3) Eurypterids are seldom found in the same chronofauna through- 

 out the world, but appear suddenly, now in one place, now in another 



